E - Common Types & Traits and the Cairo Prelude - The Cairo Programming Language

Appendix E - Common Types & Traits and the Cairo Prelude

Prelude

The Cairo prelude is a collection of commonly used modules, functions, data types, and traits that are automatically brought into scope of every module in a Cairo crate without needing explicit import statements. Cairo's prelude provides the basic building blocks developers need to start Cairo programs and writing smart contracts.

The core library prelude is defined in the lib.cairo file of the corelib crate and contains Cairo's primitive data types, traits, operators, and utility functions. This includes: Data types - felts, bools, arrays, dicts, etc. Traits - behaviors for arithmetic, comparison, serialization Operators - arithmetic, logical, bitwise Utility functions - helpers for arrays, maps, boxing, etc. The core library prelude delivers the fundamental programming constructs and operations needed for basic Cairo programs, without requiring the explicit import of elements. Since the core library prelude is automatically imported, its contents are available for use in any Cairo crate without explicit imports. This prevents repetition and provides a better devX. This is what allows you to use ArrayTrait::append() or the Default trait without bringing them explicitly into scope.

List of common types and traits

The following section provides a brief overview of commonly used types and traits when developing Cairo programs. Most of these are included in the prelude and not required to be imported explicitly - but not all of them.

Import	Path	Usage
`OptionTrait`	`core::option::OptionTrait`	`OptionTrait<T>` defines a set of methods required to manipulate optional value.
`ResultTrait`	`core::result::ResultTrait`	`ResultTrait<T, E>` Type for Starknet contract address, a value in the range [0, 2 ** 251).
`ContractAddress`	`starknet::ContractAddress`	`ContractAddress` is a type to represent the smart contract address
`ContractAddressZeroable`	`starknet::contract_address::ContractAddressZeroable`	`ContractAddressZeroable` is the implementation of the trait `Zeroable` for the `ContractAddress` type. It is required to check whether a value of `t:ContractAddress` is zero or not.
`contract_address_const`	`starknet::contract_address_const`	The `contract_address_const!` it's a function that allows instantiating constant contract address values.
`Into`	`traits::Into;`	`Into<T>` is a trait used for conversion between types. If there is an implementation of Into<T,S> for the types T and S, you can convert T into S.
`TryInto`	`traits::TryInto;`	`TryInto<T>` is a trait used for conversion between types.If there is an implementation of TryInto<T,S> for the types T and S, you can convert T into S.
`get_caller_address`	`starknet::get_caller_address`	`get_caller_address()` is a function that returns the address of the caller of the contract. It can be used to identify the caller of a contract function.
`get_contract_address`	`starknet::info::get_contract_address`	`get_contract_address()` is a function that returns the address of the current contract. It can be used to obtain the address of the contract being executed.

This is not an exhaustive list, but it covers some of the commonly used types and traits in contract development. For more details, refer to the official documentation and explore the available libraries and frameworks.